Victor Bastos was making $20,000 a year as a freelance Web developer in Lisbon, Portugal, when he started posting videos to YouTube. Already fluent in several programming languages and looking to branch into new ones, he thought making instructional videos would help him keep track of what he’d learned. “It was like an online notebook for myself,’ Bastos, 33, said. “But then I started getting a lot of subscriptions. People told me, ‘˜Your tutorials are great — why don’t you make a full course?’ ‘

Within a few months, Bastos got an email inviting him to do just that. The proposal came from an online-learning startup he had never heard of called Udemy. The offer: Host his course on Udemy’s Web-based platform, and he could charge students to take it and keep 70 percent of the revenues. Udemy would keep the other 30 percent.

Bastos accepted and got to work fleshing out a full curriculum. His goal: a one-stop course that would turn total rookies into professional Web developers. In a series of more than 220 video lectures, he lays out the basics of languages like JavaScript and MySQL via screenshare, narrating each step in a slow and soothing voice like a slightly sleepy Salman Khan. Bastos started out charging $49 but soon found that demand for his class was overwhelming and hiked the price tag to $199 while offering big discounts on Groupon to attract new customers. The formula has worked — so well that Bastos quit his job to devote himself to teaching on Udemy full-time. Since he began teaching “Become a Web Developer From Scratch!’ in late 2011, it has drawn some 7,000 students.

In that time — a year and a half — Bastos has earned $452,985.70.

He is not an outlier. Udemy, launched in 2010, reports that its top 10 instructors have generated more than $5 million in revenue so far. Many others are taking in sums that would be unheard of for a high school teacher and impressive for a college professor. A class on IT certifications and training has earned its teacher $260,000 in a little less than two years. One on video, animation and multimedia has brought in nearly $150,000 in the same period.

The focus is on technical skills, and computer classes are the biggest draw. But Udemy’s 8,000 offerings also include a smattering of courses in the humanities, social sciences and other subject areas. A yoga instructor named Dashama has earned some $45,000 in her first 11 months.

Unlike schoolteachers and professors, Udemy instructors don’t need credentials, and you don’t have to quit your day job to get started. The Silicon Valley startup says most publish their first course within two to four weeks, then spend an average of five to 15 hours per month updating course materials and responding to students’ questions. They receive some initial support from Udemy and share tips on best practices, but they can craft their own curriculum and teach basically whatever they want.

The company is quick to point out that it’s not a get-rich-quick scheme: The average instructor on the site has earned more like $7,000 in total, and only a minority quit their day jobs. “You don’t start teaching purely for the money,’ Udemy spokesman Dinesh Thiru told me. “You start teaching because you’re passionate about something.’

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